Abstract Sb-based pN heterojunction diodes at 6.2 A, consisting of narrow bandgap p -type In 0.27 Ga 0.73 Sb and wide bandgap n -type In 0.69 Al 0.41 As 0.41 Sb 0.59 , have been fabricated and measured. These diodes show excellent electrical characteristics with an ideality factor of 1.2 and high current density. S -parameter measurements and subsequent analysis show that these diodes have RC -cutoff frequencies over 1 THz, making these diodes excellent choices for high-frequency applications, such as sub-harmonic mixers for frequency conversion.